Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é o número de operações de manutenção da paz em que cada país participou por ano?
 ###Tabelas: 
CREATE TABLE if not exists peacekeeping_by_year (year INT, country TEXT, operation TEXT, troops INT); INSERT INTO peacekeeping_by_year (year, country, operation, troops) VALUES (2015, 'Country A', 'Peacekeeping Operation 1', 200); INSERT INTO peacekeeping_by_year (year, country, operation, troops) VALUES (2016, 'Country A', 'Peacekeeping Operation 1', 220); INSERT INTO peacekeeping_by_year (year, country, operation, troops) VALUES (2015, 'Country A', 'Peacekeeping Operation 2', 250); INSERT INTO peacekeeping_by_year (year, country, operation, troops) VALUES (2016, 'Country A', 'Peacekeeping Operation 2', 270); INSERT INTO peacekeeping_by_year (year, country, operation, troops) VALUES (2015, 'Country B', 'Peacekeeping Operation 1', 150); INSERT INTO peacekeeping_by_year (year, country, operation, troops) VALUES (2016, 'Country B', 'Peacekeeping Operation 1', 170); INSERT INTO peacekeeping_by_year (year, country, operation, troops) VALUES (2015, 'Country B', 'Peacekeeping Operation 2', 200); INSERT INTO peacekeeping_by_year (year, country, operation, troops) VALUES (2016, 'Country B', 'Peacekeeping Operation 2', 220);
SELECT year, country, SUM(troops) as total_troops FROM peacekeeping_by_year GROUP BY year, country;